I am in class 10th and i want to ask what to to crak iit -jee and according my level how i should study

I request you to focus on board exam rather than preparing for jee main.
Understand, the knowledge you gained during 10th is very important as it increases your basic knowledge about how the world works.
You start reading jee main as soon as you get into 11th standard.
This is the best time you can start preparing for jee main.

First of all !! I would like to say that it may be quite difficult for you to go hand by hand for both board and iit jee !!! I must recommend to join any well known institution and check yourself whether you are capable or not !! Securing good in 10th may not have a great impact on iit jee, since it is hell and heaven difference. You have to be much laborious for this ! Best of luck